Understanding the defects structures and their role on the electronic structure of graphite is an essential tool for carbon nanostructures. Defects undoubtedly alter the electronic structure and therefore chemical, optical, and other properties. Recently, graphene (single layer of graphite) and few-layer graphene showed a number of unconventional properties [1,2] and it seems to be of the great importance to understand the defects role in these materials for possible future applications.
Although graphite is one of the most extensively studied materials in scanning tunneling microscopy (STM), there are still phenomena observed on the graphite surface with STM, which cannot be well understood. Graphite often shows superperiodical features in STM experiments, which are not related to the topography of graphite. These features are called superlattices in literature [3] and are generally related to internal defects of the graphite substrate.
We report on the experimental observation of the grain boundaries of highly ordered pyrolytic graphite (HOPG) with scanning probe microscopy (SPM). Grain boundaries appear as a one-dimensional superlattice in STM. Observed superlattices extend over micrometer length and have periodicities from 0.5 nm to 10 nm with height corrugation up to 1.5 nm due to electron density effects, which is 15 times larger than graphite lattice corrugation observed with STM. The observed superlattices have been explained by a simple model based on the misalignment of two graphite grains. Low temperature scanning tunneling spectroscopy (STS) on the grain boundaries has shown localized states and enhanced charge density compared to the bare graphite surface. Moreover, the grain boundaries have been utilized as a one-dimensional template for adsorbing external atoms and clusters.
[1] K. S. Novoselov et al, Science 306, 666 (2004)
[2] K. S. Novoselov et al, Nature 438, 197 (2005)
[3] W. T. Pong and C. Durkan, J. Phys. D 38, R329 (2005)
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